Wednesday 3 March 2010

Green ragworm anyone? II

Physical Description
Ragworms have long, flattened bodies, consisting of many segments each with a pair of parapods, or swimming legs. These parapods are covered with bristles called chaete and are used for crawling and swimming. At the head end, they have a toothed proboscis, four eyes, and two pairs of antennae.

They are variable in colour, typically appearing reddish brown but turning quite green during the spawning season.

Abundant in estuaries and sandy or muddy beaches. They inhabit U- or J-shaped burrows in the sand that may stretch for around 20cm (8 inches) depth.

The ragworm is both an omnivorous scavenger and efficient predator. When scavenging, it feeds on mud, detritus, phytoplankton and plankton. It is also a active predator, rapidly shooting out its powerful jaws to catch other soft-bodied invertebrates. This species also feeds on phytoplankton by spinning a net at the top of the burrow. By undulating it's body within its burrow it causes a water current which carries phytoplankton into the sticky net. After a while it consumes the net and the particles, then spins another.

The feeding behaviour of the ragworm depends on phytoplankton densities. When densities are high, it uses its net to catch prey. When densities are low, it scavenges or actively hunts prey.
Ragworms are tuned to the lunar phase, reproducing in synchrony at distinct times in the moon phase (e.g. new or full moon, depending on the locality).

Spawning is triggered by a rise in temperature during spring. Females brood eggs within their bodies. As the eggs develop, the female's body becomes brittle and ultimately ruptures, releasing the eggs into the burrow. Males are drawn to the burrow by pheromones and discharge their sperm around the burrow entrance. The female draws this sperm down into the burrow using water currents where they fertilise the eggs. After spawning, both males and female ragworms die.
Source - BBC Science & Nature

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Forwarded to - The Irish Bass Policy Group (David McInerny, John Quinlan, Shane O Reilly, Mike Hennessy, Dr William Roche, Dr Nial O'Ma...